Mold temperature control system

ABSTRACT

A mold temperature control system that controls temperature of mold in a diecasting machine, includes temperature sensors that detect mold temperatures of individual parts of the mold, flow controllers that control instantaneous flow rates of cooling water that cools the parts of the mold, and a control device that acquires the mold temperatures detected by the temperature sensors, computes deviations between target mold temperature and the current mold temperatures at every production cycle, converts the deviations into flow rate values, and transmits the flow rate values to the flow controllers.

TECHNICAL FIELD

This invention relates to a mold temperature control system that controls the temperatures of molds of a diecasting machine.

BACKGROUND

In a diecasting machine that manufactures aluminum diecast products, because molten aluminum enters the center of the molds at every shot, temperature control by cooling is important. Especially, if the sizes of the molds increase, temperature unevenness easily occurs among different parts. In order to eliminate this temperature unevenness, heat needs to be exhausted with appropriate cooling water flow rates (or amount) for the appropriate individual parts, requiring the cooling water flow rates to be changed by the individual parts. However, because a large mold has an extremely large number of parts, its management method is complicated, and it is difficult to manage it by a normal method.

Referring to documents on the conventional management method, for example, there are a mold temperature control device of Patent Document 1 and a mold temperature control system of Patent Document 2 that only describe that the cooling water flow rates are adjusted according to the mold temperatures, which is a level of management method variable according to at most 2-3 divided zones. Although there are many cases of temperature management method including other documents, few currently deal with the management method for molds having many systems.

In fact, there are up to 120 systems of mold cooling holes in a 4-cylinder engine block, and the heat input differs between a fixed mold and a movable mold. Also, because the mold size is as large as a square having sides of 2-3 meters in size, it is impossible to judge the temperature of which part of each system the control should target. Furthermore, if parts of the 120 systems were individually controlled so that the mold temperatures became constant among the systems, due to mutual interferences with neighboring systems, no presumed control or expected temperature management could be performed, which was a problem.

RELATED ART

[Patent Doc.1] JP Laid-Open Patent Application Publication H11-47883

[Patent Doc.2] JP Laid-Open Patent Application Publication H10-109343

MAIN OBJECT(S) OF THE INVENTION

Then, this invention has been made considering this kind of problem, and its objective is to offer a mold temperature control system that allows precise temperature management even for large molds with many systems.

SUMMARY

To solve the subject(s), the present invention includes features following.

A mold temperature control system, which is described in the application, that controls temperature of mold in a diecasting machine, includes temperature sensors that detect mold temperatures of individual parts of the mold, flow controllers that control instantaneous flow rates of cooling water that cools the parts of the mold, and a control device that acquires the mold temperatures detected by the temperature sensors, computes deviations between target mold temperature and the current mold temperatures at every production cycle, converts the deviations into flow rate values, and transmits the flow rate values to the flow controllers.

In a preferred embodiment of the mold temperature control system, the control device compares a representative mold temperature and the current mold temperature in each of the parts of the mold, computes the deviations, and determines correction values for flow rates based on the deviations.

In another preferred embodiment of the mold temperature control system, the correction values are the same at all the parts of the mold, and are used to adjust whole flow rate values by a constant amount.

In another preferred embodiment of the mold temperature control system, the correction values are different among the parts of the mold, the correction values are regarded as 100% at a previous production cycle, and the flow rate values are adjusted by individual ratios for the parts with respect to the correction values.

In another preferred embodiment of the mold temperature control system, the control device has a flow rate program set up in advance that makes the flow rates variable during the production cycle, and adds the correction value without changing a waveform of the flow rate program.

In another preferred embodiment of the mold temperature control system, the control device divides one period of the production cycle into three time zones of T1, T2, and T3 by a timer, sets the flow rates of T1 and T3 to predetermined flow rates, and corrects the flow rate of T2 by acquiring the mold temperature after finishing the production cycle and computing the flow rate value for a next production cycle.

In another preferred embodiment of the mold temperature control system, the correction is performed by increasing or decreasing the flow rate value in T2.

In another preferred embodiment of the mold temperature control system, defining that one period of the production cycle is T4, the correction is performed by increasing or decreasing time of T2 within prescribed time of T4.

In another preferred embodiment of the mold temperature control system the mold is configured with two sub parts, one of which is a fixed mold that is fixed to a body of the diecasting machine, and the other of which is a movable mold that is repeatedly movable with respect to the body, and the temperature sensors are disposed on one of the fixed mold and the movable mold, or both of the fixed mold and movable mold.

ADVANTAGE(S) OF THE INVENTION

This invention has an effect that its installation space and cost can be suppressed to realize the mold temperature control of many cooling systems by using flow controllers that control the instantaneous flow rates of cooling water. Also, by changing within one shot the flow rates of cooling water that were controlled as a constant flow rate at the time of production, it has effects of solidifying speed can be changed and improving the product characteristics. Furthermore, it also allows adjusting the height of temperature fluctuations within one shot at the time of production, having an effect of improving the product quality and yield in manufacturing thin or complex shaped product.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a conceptual drawing showing the whole configuration of a mold temperature control system of this invention.

FIG. 2 is a partial cross-sectional view showing the structure of a flow rate control unit in the same system.

FIG. 3 is a cross-sectional view showing the internal structure of flow controllers in the same system.

FIG. 4 is a flow chart showing a control method by the same system.

FIG. 5 is an explanatory diagram showing an example of mold temperature characteristic data.

FIG. 6 is a plot showing the relationship between mold temperature and cooling water flow rate through production cycles.

FIG. 7 is a block diagram showing the details of an arithmetic process.

FIG. 8 is a table showing the relationship between reference temperature and reference flow rate.

FIG. 9 is a plot showing an example of flow rate correction values.

FIG. 10 is a plot showing an example of adding a correction value to the waveform of a flow rate program.

FIG. 11 is a plot showing a correction example of increasing the flow rate value in T2 in a production cycle.

FIG. 12 is a plot showing a correction example of increasing the time of T2 within the prescribed time of T4 in a production cycle.

DETAILED DESCRIPTIONS OF THE EMBODIMENTS

Below, an embodiment of this invention is explained referring to drawings.

As shown in FIG. 1, a mold temperature control system 1 of this embodiment is a system that controls the temperatures of molds 3 by changing the flow rate of cooling water that was controlled to be a constant flow rate at the time of production in a diecasting machine 2 that produces (casts) aluminum diecast products. The molds 3 constitute part of the diecasting machine 2 and consists of a fixed mold 4 installed on an injection device and a movable mold 5 installed on a mold clamping device.

Attached to parts of the molds 3 (the fixed mold 4 and the movable mold 5) are temperature sensors 6 (˜6 n), each of which comprises a thermocouple or a temperature measuring resistor. The temperature sensors 6 detect in real time the maximum, minimum, average, and current temperatures of the molds 3 within the production cycle. The detected temperature information of the molds 3 is converted into electric signals and output to a control device 7 that performs an arithmetic process mentioned below.

Installed outside the diecasting machine 2 is a cooling water circulating device 8 that circulates cooling water as a means to adjust the temperatures of the molds 3. The cooling water circulating device 8 comprises a cooling tower 9, a heat exchanger 10, a tank 11, and a pump 12. Water inside the tank 11 is cooled through the heat exchanger 10 by the cooling tower 9. The cooling water is supplied to cooling water holes installed on individual parts of the molds 3 via a water supply pipe 13 by the pump 12, and circulates to the tank 11 via a return pipe 14.

Attached to each of the molds 3 (the fixed mold 4 and the movable mold 5) is a flow rate control unit 15. As shown in FIG. 2, each of the flow rate control units 15 comprises a manifold 16 connected to the water supply pipe 13, and a group of multiple flow controllers 17 (˜17 n) installed as a series to the manifold 16. The manifold 16 has cooling water from the water supply pipe 13 introduced into a cavity 18 via a strainer (not shown), branched at multiple ports 19 (˜19 n), and supplied to the individual flow controllers 17 (˜17 n).

The flow controllers 17 are flow control devices that control the instantaneous flow rates of cooling water that cools the individual parts of the molds 3 (the fixed mold 4 and the movable mold 5). As shown in FIG. 3, the flow controllers 17 each comprise a flow rate adjusting valve 20, a flow rate measuring part 21, and a control part 22, and are connected to the ports 19 of the manifold 16 through two joint adapters 23 and 23 coupled alternately.

Adopted by the flow rate adjusting valve 20 is a ball valve mechanism in this embodiment. This ball valve mechanism has a valve element 25 connected to the rotation shaft of a motor actuator 24, and a ball part 26 that is installed on the tip of the valve element 25 and can adjust the valve opening degrees.

Adopted by the flow rate measuring part 21 is an impeller-type flow meter in this embodiment. This impeller-type flow meter has an impeller 27 supported rotatably in a flow path, and a sensor unit 28 that measures the rotation rate of the impeller 27. The sensor unit 28 includes a sensor board 29, a GMR sensor 30, and a bias magnet 31, measures the rotation rate of the impeller 27 detected by the GMR sensor 30, and outputs a pulse signal (rotation rate signal) according to the measurement result to the control part 22.

The control part 22 is a microcomputer. The control part 22 controls the motor actuator 24 based on the rotation rate signal output from the flow rate measuring part, and feedback-controls (PID-controls) the opening of the flow rate adjusting valve 20.

Mentioned above is the configuration of the mold temperature control system 1 of this embodiment, and its control method is explained next referring to FIG. 4.

<S401 (Step 401)>

First, the system is started in the control device 7.

<S402>

In performing temperature control, mold temperature characteristic data are prepared in advance from parameters for the cooling water flow rates with an appropriate mold temperature distribution. First, cooling water is adjusted to realize an ideal mold temperature distribution, and temperature at that time is regarded as a reference temperature (SV), which is a target, at the time of control. Also, the cooling water flow rates are recorded, and the flow rate values are regarded as reference flow rates (StFWn).

Next, as shown FIG. 5, cooling water is grouped by the parts of the molds 3. In each of the groups, a part (cooling No.) that becomes a reference position is decided. In adjusting the temperature of the individual parts, the reference position should preferably be a part that is closer to the center where temperature changes can easily appear and attaching the temperature sensor 6 is easy. Note that if the mold temperature characteristic data are already prepared, only reading the existing data is performed.

<S403>

Once a preheating shot by the diecasting machine is finished, and a production is started, a mold temperature control state is entered.

<S404>

Mold temperature control (arithmetic process) is started upon a process trigger signal.

<S405>

Time is measured with the process trigger signal intervals as the production cycle intervals. Setting this time measurement result as the arithmetic cycle, an adjustment is made so that the actual production cycle coincides with the arithmetic cycle.

<S406>

The mold temperatures are detected by the temperature sensors 6. As shown in FIG. 6, as the mold temperature, the maximum temperature (MAX), the minimum temperature (MIN), the average temperature (AVE), and the current temperature (DIR) within the production cycle are acquired and retained, and one of those temperatures is set as the mold temperature (PV) in performing the arithmetic process.

<S407>

The arithmetic cycle is monitored.

<S408>

The reference temperature (SV) that is a target (or target mold temp.), the mold temperature (PV), and in this embodiment the current temperature (DIR) are monitored in each cycle, the two temperatures are compared to compute SV-PV, and a PID calculation is executed.

<S409>

A flow rate value conversion process is performed to convert the results obtained by the PID calculations into the flow rate values of the flow controllers 17.

<S410>

The flow rate values obtained by the flow rate value conversion process are transferred from the control device 7 to the flow controllers 17.

<S411>

The production cycle in a diecasting process can develop a time delay due to a product extracting process etc., causing a shift between the production cycle and the arithmetic process according to the preset arithmetic cycle. Therefore, the input interval of the process trigger is measured as the production cycle interval, and a correction to the arithmetic cycle is performed.

<S412>

After the production is finished, the system is stopped.

As mentioned above, the arithmetic process is performed after the arithmetic cycle (time is up), and the arithmetic process is performed periodically after the production is started until the production is finished. Note that this arithmetic process is performed only for the reference point of each of the cooling water groups.

Here, to explain further details of the arithmetic process, as shown in FIG. 7, the set flow rate value for the reference point is obtained by converting the PID-calculated value as it is into a flow rate value. The set flow rate values for the other points than the reference point are obtained by utilizing the increase/decrease rate (IDr) between the current set flow rate value (SvFWn) and the reference flow rate (StFWn) of the reference point.

As shown in FIG. 8, it is assumed that the reference temperature (SV) is 122° C. and the reference flow rate (StFW002) is 1.7 L/min at the reference point (Cooling No. C002), and the reference flow rate (StFW003) at Cooling No. C003 in the same group is 2.5 L/min. At this time, if the temperature of the reference point (Cooling No. C002) at a point of time is 145° C., and the set flow rate value (SvFW002) is 2.3 L/min as an arithmetic result, the set flow rate of Cooling No. C003 in the same group is computed in the following manner.

$\begin{matrix} {{IDr} = {{SvFW}\;{002/{StFW}}\; 002}} \\ {= {2.3/1.7}} \\ {\cong 1.35} \end{matrix}$ $\begin{matrix} {{{SvFW}\; 003} = {{StFW}\; 003*{IDr}}} \\ {= {2.5*1.35}} \\ {\cong {3.38\mspace{14mu}\text{L/min}}} \end{matrix}$

Next, explained are corrections to the flow rate values. The flow rates of the individual parts determined based on the mold temperature characteristic data reflect just the optimal allocation in the current environment. Because the temperature of molten aluminum, the ambient temperature, and the temperature of cooling water from the cooling tower 9 vary depending on season and time of day, even if the predetermined flow rates are given, the mold temperatures vary through time due to this external disturbance. In order to correct for the external disturbance, although the cooling water flow rates need to be adjusted, it should be noted that the heat exhaust allocation must not be changed. If this allocation is changed, the whole temperature distribution will collapse, which should be noted. Therefore, it is important that increasing or decreasing the flow rates for temperature control should be performed so as not to change the allocation.

In this embodiment, after supplying cooling water of the flow rates determined based on the mold temperature characteristic data to the individual parts of the molds 3, deviations between the representative mold temperatures and the current mold temperatures are computed, and correction values for the flow rates are determined from the deviations. These correction values are just correction values for the whole, and regarding these correction values as variation rates (%), these variation rates are given to the current flow rates of the individual systems (their initial values are predetermined flow rates), and the flow rates are increased or decreased to perform the temperature control of the molds 3.

Here, as shown in FIG. 9A, the correction values can be made the same at all the parts (systems) of the molds 3 to adjust (correct) the whole flow rate values by the same amount. Also, as shown in FIG. 9B, the correction values can be made different among the individual parts (systems) of the molds 3 to adjust the ratios by the parts (systems). For example, the values at the previous production cycle can be regarded as 100%, and the flow rate values can be adjusted from that value according to the ratios for the individual parts (systems).

In this case, the flow rate within one shot of the production cycle can be constant for each molding shot. Thereby, the detection of the mold temperatures can be performed only for a representative value (reference point), and there is also only one correction value. Therefore, even if the number of systems increases, the management method does not change, and even if the sizes of the molds 3 increase, temperature management can be easily performed. Regarding the number of the temperature sensors 6, multiple (2-3 pieces) of them can be attached, and one value can be derived by weighted averaging. Also, regarding the computation of the correction values, although the PID calculation was adopted above, another method that computes them from another data table (step control) can be adopted. Note that because the molds 3 have the fixed mold 4 and the movable mold 5 independently, there are two representative temperatures. Therefore, the fixed mold 4 and the movable mold 5 should desirably be controlled with individual representative temperatures so that their temperatures become constant.

Also, if the flow rate during the production cycle can be varied in a more complex manner, it becomes possible to offer better quality products with a shorter cycle time. For example, as shown in FIG. 10, the control device can have a flow rate program set up in advance that varies the flow rate during the production cycle, and the flow rate can be increased or decreased by adding a correction value without changing the waveform of the flow rate program. Regarding its adjustment margin, the correction values can either be the same as in FIG. 9A or vary according to the ratios as in FIG. 9B.

Also, the embodiment explained below is to change the flow rates of cooling water using three timers. As shown in FIG. 11, one period of the production cycle is divided into three time zones of T1, T2, and T3 in this order by the three timers. Then, the flow rates in T1 and T3 are set to a predetermined flow rate, and regarding the flow rate in T2, the mold temperature after finishing the production cycle is acquired, and the flow rate in T2 for the next production cycle is computed by the PID calculation.

Because a large mold with many systems is difficult to manage, the mold temperature distribution is imaged in advance by an infrared thermographic camera (not shown) or the like, and the cooling water flow rates of the individual systems are determined in advance for the optimal mold temperature distribution. Also, the temperature sensors 6 can also be installed on representative parts, and the flow rates in T2 can be individually corrected for the systems so that the temperatures become constant, thereby the mold temperature management and the temperature waveform adjustment can be easily performed.

Note that although in this embodiment three time zones of T1, T2, and T3 are used, instead, only two time zones of T1 and T2 or T2 and T3 can be used for changing the cooling water flow rates. Also, regarding the correction, although the flow rate value in T2 is increased or decreased for performing the correction, as shown in FIG. 12, denoting one period of the production cycle as T4, the time of T2 can be increased or decreased within the prescribed time of T4 for performing the correction.

The embodiment above is to adjust the waveform curve of the mold temperature within the production cycle. By adjusting the waveform curve in this manner, it becomes possible to adjust the finished state of the products (hot water wrinkles and sink marks due to solidification). Therefore, not only the product yield improves, but also the shot time of one cycle will eventually be reduced. Managing these becomes especially indispensable for thin-walled products.

LEGENDS

-   1: mold temperature control system -   2: diecasting machine -   3: mold -   4: fixed mold -   5: movable mold -   6: temperature sensor -   7: control device -   8: cooling water circulating device -   9: cooling tower -   10: heat exchanger -   11: tank -   12: pump -   13: water supply pipe -   14: return pipe -   15: flow rate control unit -   16: manifold -   17: flow controller -   18: cavity -   19: port -   20: flow rate adjusting valve -   21: flow rate measuring part -   22: control part -   23: joint adapter -   24: motor actuator -   25: valve element -   26: ball part -   27: impeller -   28: sensor unit -   29: sensor board -   30: GMR sensor -   31: bias magnet 

What is claimed is:
 1. A mold temperature control system that controls temperature of a mold in a diecasting machine, comprising: temperature sensors that detect mold temperatures of individual parts of the mold, flow controllers that control instantaneous flow rates of cooling water that cools the parts of the mold, and a control device that acquires the mold temperatures detected by the temperature sensors, computes deviations between a target mold temperature and the current mold temperatures at every production cycle, converts the deviations into flow rate values, and transmits the flow rate values to the flow controllers.
 2. The mold temperature control system according to claim 1, wherein the control device compares a representative mold temperature and the current mold temperature in each of the parts of the mold, computes the deviations, and determines correction values for flow rates based on the deviations.
 3. The mold temperature control system according to claim 2, wherein the correction values are the same at all the parts of the mold, and are used to adjust whole flow rate values by a constant amount.
 4. The mold temperature control system according to claim 2, wherein the correction values are different among the parts of the mold, the correction values are regarded as 100% at a previous production cycle, and the flow rate values are adjusted by individual ratios for the parts with respect to the correction values.
 5. The mold temperature control system according to claim 3, wherein the control device has a flow rate program set up in advance that makes the flow rates variable during the production cycle, and adds the correction value without changing a waveform of the flow rate program.
 6. The mold temperature control system according to claim 4, wherein the control device has a flow rate program set up in advance that makes the flow rates variable during the production cycle, and adds the correction value without changing a waveform of the flow rate program.
 7. The mold temperature control system according to claim 1, wherein the control device divides one period of the production cycle into three time zones of T1, T2, and T3 by a timer, sets the flow rates of T1 and T3 to predetermined flow rates, and corrects the flow rate of T2 by acquiring the mold temperature after finishing the production cycle and computing the flow rate value for a next production cycle.
 8. The mold temperature control system according to claim 7, wherein the correction is performed by increasing or decreasing the flow rate value in T2.
 9. The mold temperature control system according to claim 7, wherein defining that one period of the production cycle is T4, the correction is performed by increasing or decreasing time of T2 within prescribed time of T4.
 10. The mold temperature control system according to claim 1, wherein the mold is configured with two sub parts, one of which is a fixed mold that is fixed to a body of the diecasting machine, and the other of which is a movable mold that is repeatedly movable with respect to the body, and the temperature sensors are disposed on one of the fixed mold and the movable mold, or both of the fixed mold and movable mold. 